The present invention concerns apparatus for controlling the flow of cooling fluid in a cooling system for an internal combustion engine, and more particularly, a thermostatic mixing valve in an engine cooling system having a radiator, a circulating pump, and fluid connections for circulating cooling liquid from the engine through the radiator and back to the engine, and from an outlet of the engine directly back to an inlet of the engine, bypassing the radiator. The thermostatic mixing valve includes inlets for receiving the cooling liquid from the radiator and from the engine, and a thermostatic element which is sensitive to the temperature of a mixture of the incoming liquids and, thereby, determines the proportions of the two liquids which flow through the mixing valve.
The liquid flowing from the radiator is relatively cold and the liquid flowing from the outlet of the engine is relatively hot, so that "cold liquid" and "hot liquid" can be used to identify the liquids coming from the two sources. However, there are situations where the liquid coming from the radiator, the liquid coming from the engine outlet, and the liquid coming from the outlet of the thermostatic mixing valve are all at the same temperature, for example, when the engine is cold. There are also periods when the socalled hot liquid is at a relatively low temperature, such as during the engine starting period.
A mixing valve of the type mentioned above is described, for example, in French Patent No. FR A - 1 472 712. In that valve, the thermostatic element is sensitive not only to the mixed liquid temperature but also to the cold liquid temperature, and it controls two separate poppets which calibrate, respectively, the hot liquid flow and the cold liquid flow to be mixed (see FIG. 3 of the French patent). It can also control a sliding sleeve opening a direct communication between hot liquid and mixed liquid (FIG. 2 of the French patent).
French Patent No. FR A - 2 434 723 discloses a mixing valve having a slide which increases the inlet area of the relatively hot liquid while decreasing the inlet area of the relatively cold liquid and vice versa, but the valve is installed, not in the engine cooling system, but in an auxiliary liquid circuit passing through an air-liquid heat exchanger for the hot air heating of the passenger compartment.